铁是在许多生化反应中用作辅因子的过渡金属。在细菌中,铁稳态涉及Fur介导的铁摄取系统的去抑制,如铁螯合化合物铁载体。在这项工作中,我们鉴定并表征了控制环境机会病原体中铁载体的新型调控系统。筛选10,000个转座子突变体文库的铁载体光晕鉴定了七种可能的调节系统,这些系统参与了紫罗兰C.C.中铁载体介导的铁稳态。进一步的表征揭示了控制铁载体的调节级联,该铁载体涉及在群体感应(QS)系统CviIR上游起作用的转录因子VitR。调节因子VitR的突变导致铁载体晕的增加,和生物膜的减少,紫罗兰素,和蛋白酶生产。我们确定这些效应是由于VitR依赖性的vios去抑制而发生的。增加的VioS导致通过蛋白质-蛋白质相互作用直接抑制CviR调节剂。的确,cviR的插入突变和cviI和cviR的无效突变导致铁载体光晕的增加。cviI和cviR突变体的RNA-seq揭示CviR调节CviI依赖性和CviI非依赖性调节子。经典的QS依赖过程(紫罗兰素,蛋白酶,和抗生素)在高细胞密度下被CviI和CviR激活。然而,与铁稳态和许多其他过程相关的基因受到CviR而不是CviI的调节,这表明CviR的行为没有其典型的CviI自动诱导剂。我们的数据揭示了涉及QS的复杂调节级联反应,该级联反应控制紫菜中铁载体介导的铁稳态。重要铁螯合化合物铁载体在细菌铁获取中起主要作用。这里,我们采用基因筛选来鉴定紫罗兰色杆菌中的新型铁载体调节系统,一种机会性的人类病原体。许多具有增加的铁载体光晕的突变体在编码转录因子的基因中具有转座子插入,包括一个叫做VitR的新型调节器,和CviR,法定感应(QS)系统CviIR的调节器。我们发现VitR在该途径的上游,并作为vioS的专用阻遏物,它编码直接的CviR抑制蛋白。的确,vitR突变体的所有QS相关表型均在vitRvioS突变体中获救.在高细胞密度下,CviIR激活了经典的QS依赖过程(紫罗兰素,蛋白酶,和抗生素生产)。然而,与铁稳态以及III型和VI型分泌系统相关的基因受CviR以CviI或细胞密度无关的方式调节。我们的数据揭示了紫罗兰杆菌中整合QS和铁载体的复杂调节级联。
Iron is a transition metal used as a cofactor in many biochemical reactions. In bacteria, iron homeostasis involves Fur-mediated de-repression of iron uptake systems, such as the iron-chelating compounds siderophores. In this work, we identified and characterized novel regulatory systems that control siderophores in the environmental opportunistic pathogen Chromobacterium violaceum. Screening of a 10,000-transposon mutant library for siderophore halos identified seven possible regulatory systems involved in siderophore-mediated iron homeostasis in C. violaceum. Further characterization revealed a regulatory cascade that controls siderophores involving the transcription factor VitR acting upstream of the quorum-sensing (QS) system CviIR. Mutation of the regulator VitR led to an increase in siderophore halos, and a decrease in biofilm, violacein, and protease production. We determined that these effects occurred due to VitR-dependent de-repression of vioS. Increased VioS leads to direct inhibition of the CviR regulator by protein-protein interaction. Indeed, insertion mutations in cviR and null mutations of cviI and cviR led to an increase of siderophore halos. RNA-seq of the cviI and cviR mutants revealed that CviR regulates CviI-dependent and CviI-independent regulons. Classical QS-dependent processes (violacein, proteases, and antibiotics) were activated at high cell density by both CviI and CviR. However, genes related to iron homeostasis and many other processes were regulated by CviR but not CviI, suggesting that CviR acts without its canonical CviI autoinducer. Our data revealed a complex regulatory cascade involving QS that controls siderophore-mediated iron homeostasis in C. violaceum.IMPORTANCEThe iron-chelating compounds siderophores play a major role in bacterial iron acquisition. Here, we employed a genetic screen to identify novel siderophore regulatory systems in Chromobacterium violaceum, an opportunistic human pathogen. Many mutants with increased siderophore halos had transposon insertions in genes encoding transcription factors, including a novel regulator called VitR, and CviR, the regulator of the quorum-sensing (QS) system CviIR. We found that VitR is upstream in the pathway and acts as a dedicated repressor of vioS, which encodes a direct CviR-inhibitory protein. Indeed, all QS-related phenotypes of a vitR mutant were rescued in a vitRvioS mutant. At high cell density, CviIR activated classical QS-dependent processes (violacein, proteases, and antibiotics production). However, genes related to iron homeostasis and type-III and type-VI secretion systems were regulated by CviR in a CviI- or cell density-independent manner. Our data unveil a complex regulatory cascade integrating QS and siderophores in C. violaceum.